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3rd Generation WCDMA / UMTSWireless Network

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M.TECH COS

UMTS:

This is the successor of 2G (GSM) network specification in which much more consideration was given for higher data rates to support a variety of applications by mobile users.

UMTS uses a totally different air interface for radio communications hence different from 2G in many ways and require specialized handsets for the new networks based on UMTS.

WCDMA is the air interface technology being used in UMTS networks.

The network architecture has a core network and access network known as UTRAN (Universal Terrestrial Radio Access Network) which consists of node B and RNC (Radio Network Controller) analogues to BTS and BSC in 2G networks.

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W-CDMA:

W-CDMA or WCDMA (Wideband Code Division Multiple Access), along with UMTS-FDD, UTRA-FDD, or IMT-2000 CDMA Direct Spread is an air interface standard found in 3G mobile telecommunications networks.

It supports conventional cellular voice, text and MMS services, but can also carry data at high speeds, allowing mobile operators to deliver higher bandwidth applications including streaming and broadband Internet access.

The main feature behind WCDMA technique is that the 5MHz channel bandwidth is used to send the data signals over the air interface and in order to achieve this original signal is mixed with a pseudo random noise code which is also known as Direct Sequence CDMA.

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This is a unique code for each user and only the users who are having the correct code can decode the message.

So with the high frequency associated with the pseudo signal, original signal is modulated in to higher frequency signal and due to high spectrum original signal spectral components sink in the noise.

Frequency band assigned for FDD-WCDMA consists of 1920-1980 and 2110-2170 MHz Frequency paired uplink and downlink with 5MHz band width channels and duplex distance is 190 MHz s.

Originally WCDMA uses QPSK as the modulation scheme

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Evolution : From 2G to 3G

Source : Northstream, Operator Options for 3G Evolution, Feb 2003.

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Evolution : From 2G to 3G

Fully specified and world-widely valid,Major interfaces should be standardized and open.

Supports multimedia and all of its components.

Wideband radio access.

Services must be independent from radio access technology and is not limited by the network infrastructure.

Primary Requirements of a 3G Network

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Standardization of WCDMA / UMTS

Multiple Access Method DS-CDMA

Duplexing Method FDD/TDD

Base Station Synchronization Asychronous Operation

Channel Separation 5MHz

Chip Rate 3.84 Mcps

Frame Length 10 ms

Service Multiplexing Multiple Services with different QoS Requirements Multiplexed on one Connection

Multirate Concept Variable Spreading Factor and Multicode

Detection Coherent, using Pilot Symbols or Common Pilot

Multiuser Detection, Smart Antennas

Supported by Standard, Optional in Implementation

WCDMA Air Interface, Main Parameters

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UMTS System Architecture

USIM

ME

Node B

Node BRNC

Node B

Node BRNC

MSC/VLR

GMSC

SGSN GGSN

HLR

UTRAN CNUE

Ext

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Cu

Uu Iu

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UMTS Bearer Services

TE MT UTRANCN IuEDGENODE

CNGateway TE

End-to-End Service

External BearerService

Radio Access BearerService

BackboneNetwork Service

UTRAFDD/TDDService

TE/MT LocalBearer Sevice

UMTS Bearer Service

CN BearerService

Radio BearerService

Iu BearerService

Physical BearerService

UMTS

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WCDMA Air Interface

Wideband CDMA, Overview

DS-CDMA, 5 MHz Carrier Spacing,

CDMA Gives Frequency Reuse Factor = 1

5 MHz Bandwidth allows Multipath Diversity using Rake Receiver

Variable Spreading Factor (VSF) to offer Bandwidth on Demand (BoD) up to 2MHz

Fast (1.5kHz) Power Control for Optimal Interference Reduction

Services multiplexing with different QoS Real-time / Best-effort 10% Frame Error Rate to 10-6 Bit Error Rate

UE UTRAN CN

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WCDMA Air Interface UE UTRAN CN

Direct Sequence Spread Spectrum

User 1

User N

Spreading

SpreadingReceived

Despreading

Narrowband

Code Gain

Frequency Reuse Factor = 1

Wideband

Wideband

5 MHz Wideband Signal allows Multipath Diversity with Rake Receiver

Wideband

Narrowband

f

f

ff

f

f

t

t

Multipath Delay Profile Variable Spreading Factor (VSF)

User 1

Spreading : 256

Widebandf f

User 2

Spreading : 16

Widebandf f

VSF Allows Bandwidth on Demand. Lower Spreading Factor requires Higher SNR, causing Higher Interference in exchange.

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WCDMA Air Interface UE UTRAN CN

Mapping of Transport Channels and Physical Channels

Broadcast Channel (BCH)

Forward Access Channel (FACH)

Paging Channel (PCH)

Random Access Channel (RACH)

Dedicated Channel (DCH)

Downlink Shared Channel (DSCH)

Common Packet Channel (CPCH)

Primary Common Control Physical Channel (PCCPCH)

Secondary Common Control Physical Channel (SCCPCH)

Physical Random Access Channel (PRACH)

Dedicated Physical Data Channel (DPDCH)

Dedicated Physical Control Channel (DPCCH)

Physical Downlink Shared Channel (PDSCH)

Physical Common Packet Channel (PCPCH)

Synchronization Channel (SCH)

Common Pilot Channel (CPICH)

Acquisition Indication Channel (AICH)

Paging Indication Channel (PICH)

CPCH Status Indication Channel (CSICH)

Collision Detection/Channel Assignment Indicator Channel (CD/CA-ICH)

Highly Differentiated Types of Channels enable best combination of Interference Reduction, QoS and Energy Efficiency,

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UTRAN UE UTRAN CN

Node B

Node BRNC

Node B

Node BRNC

IubIur

UTRAN

RNS

RNS

Two Distinct Elements :

Base Stations (Node B)Radio Network Controllers (RNC)

1 RNC and 1+ Node Bs are group together to form a Radio Network Sub-system (RNS)

Handles all Radio-Related Functionality

Soft Handover Radio Resources Management Algorithms

Maximization of the commonalities of the PS and CS data handling

UMTS Terrestrial Radio Access Network, Overview

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Core Network UE UTRAN CN

MSC/VLR

GMSC

SGSN GGSN

HLR

CN

Ext

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Core Network, Overview

Changes From Release ’99 to Release 5

A Seamless Transition from GSM to All-IP 3G Core Network

Responsible for Switching and Routing Calls and Data Connections within, and to the External Networks

(e.g. PSTN, ISDN and Internet)

Divided into CS Network and PS Network

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Core Network UE UTRAN CN

MSC/VLR

GMSC

SGSN GGSN

HLR

Ext

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Iu-cs

Core Network, Release ‘99

CS Domain :

Mobile Switching Centre (MSC) Switching CS transactions

Visitor Location Register (VLR) Holds a copy of the visiting user’s

service profile, and the precise info of the UE’s location

Gateway MSC (GMSC) The switch that connects to

external networks

PS Domain :

Serving GPRS Support Node (SGSN) Similar function as MSC/VLR

Gateway GPRS Support Node (GGSN) Similar function as GMSC

Register :

Home Location Register (HLR)

Stores master copies of users service profiles

Stores UE location on the level of MSC/VLR/SGSN

Iu-ps

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Core Network UE UTRAN CN

MGW MGW

SGSN GGSN

ExternalNetworks

Iu-cs

Core Network, R5

1st Phase of the IP Multimedia Subsystem (IMS)

Enable standardized approach for IP based service provision

Media Resource Function (MRF) Call Session Control Function (CSCF) Media Gateway Control Function

(MGCF)

CS Domain :

MSC and GMSC Control Function, can control multiple

MGW, hence scalable MSG

Replaces MSC for the actual switching and routing

PS Domain :

Very similar to R’99 with some enhancements

Iu-ps

MSC GMSCIu-cs

MRF CSCF

HSS

MGCF

Services & Applications

Services & ApplicationsIMS

Function

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Radio Resources Management

Network Based Functions

Admission Control (AC) Handles all new incoming traffic. Check whether new connection can be admitted to

the system and generates parameters for it.

Load Control (LC) Manages situation when system load exceeds the threshold and some counter

measures have to be taken to get system back to a feasible load.

Packet Scheduler (PS) Handles all non real time traffic, (packet data users). It decides when a packet

transmission is initiated and the bit rate to be used.

Connection Based Functions

Handover Control (HC) Handles and makes the handover decisions. Controls the active set of Base Stations of MS.

Power Control (PC) Maintains radio link quality. Minimize and control the power used in radio interface, thus maximizing the call

capacity.

Source : Lecture Notes of S-72.238 Wideband CDMA systems, Communications Laboratory, Helsinki University of Technology

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Connection Based Function

Power Control

Prevent Excessive Interference and Near-far Effect

Open-Loop Power Control Rough estimation of path loss from

receiving signal Initial power setting, or when no

feedback channel is exist

Fast Close-Loop Power Control Feedback loop with 1.5kHz cycle to

adjust uplink / downlink power to its minimum

Even faster than the speed of Rayleigh fading for moderate mobile speeds

Outer Loop Power Control Adjust the target SIR setpoint in base

station according to the target BER Commanded by RNC

Fast Power Control

If SIR < SIRTARGET, send “power up” command to MS

Outer Loop Power Control

If quality < target, increases SIRTARGET

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Connection Based Function

Handover

Softer Handover

A MS is in the overlapping coverage of 2 sectors of a base station

Concurrent communication via 2 air interface channels

2 channels are maximally combined with rake receiver

Soft Handover

A MS is in the overlapping coverage of 2 different base stations

Concurrent communication via 2 air interface channels

Downlink: Maximal combining with rake receiver

Uplink: Routed to RNC for selection combining, according to a frame reliability indicator by the base station

A Kind of Macrodiversity

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WCDMA vs cdma2000

Some of the Major Differences

WCDMA cmda2000 Remarks

Spread Sprectrum Technique

5Mhz Wideband DS-SS

Multicarrier,3x1.25MHz Narrowband DS-SS, 250kHz Guard Band

Multicarrier does not requires a contiguous spectral band. Both scheme can achieve similar performance

Chip Rates 3.84Mcps 3.6864Mcps (1.2288 per carrier)

Chip Rate alone does not determine system capacity

Frame Lengths 10ms 20ms for data, 5ms for control

Response and efficiency tradeoff

Power Control Rate 1.5kHz 800Hz Higher gives better link performance

Base Station Synchronization

Asynchronous Synchronized Asynchronous requires not timing reference which is usually hard to acquire.Synchronized operation usually gives better performance

Adopted by Telecommunications Industry Association, backward compatible with IS-95, lately moved to 3GPP2 (in contrast to 3GPP for WCDMA) as the CDMA MultiCarrier member of the IMT-2000 family of standard

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